My heart would inquire of your hands pale and fine... If they'd grasp it gently, to hold like a rose... (first dialogue option)

Or treat it as a morsel upon which to dine? (second dialogue option)

At this point, the player is in control of Dandelion rather than the witcher. As Dandelion you can either choose to enter the succubus' lair by means of a trap door which opens or inform Geralt who takes over the investigation. After talking with the succubus, you will be able to choose to side with either the succubus or Ele'yas.

To side with the succubus, you'll need to inform Iorveth and for that, you'll need the metal shard extracted from the body earlier in the catacombs using the surgical tools bought from Felicia in the market.

Either side has its advantages but you may want to side with the succubus in lesser difficulty modes. If you have played your cards right you should already have a better weapon (Kaedweni black sword) and a Robust red meteorite sword. The Kayran's chest piece could be considered better than Thyssen's armor but the sword may still be considerable.

High difficulty players (Dark / Insane) will have long had access to better equipment and could likely use the extra orens from siding with Ele'yas and looting the succubus.

Sometimes even if you have the quest and tools the corpse mouse interaction wont open, can't be analyzed.

Sometimes Iorveth will "disappear" and thus not be available if Geralt wants to hand in the murder evidence.

This can sometimes be resolved by meditating in Iorveth's quarters (located in the outskirts of Vergen, north-west of town) until after midnight, then quicksaving, then reloading that quicksave immediately after. Iorveth should then reappear next to his bedroll. [1]

And now let me tell you how I solved a crime in Vergen with a bit of help from Geralt, who started the whole thing by talking to the elf Ele'yas. Ele'yas thought he would need a witcher, but had no idea that a poet would prove to be key to the case! Young men, both elves and humans, were being murdered in Vergen. The elf said their bodies were being found near a burned village located at the mouth of the gully leading to Vergen, and subsequently being interred in catacombs beyond the town. Geralt took it all in and began to wonder if he should go to the crime scene or the burial site.

As Geralt searched the burned village for clues, he could not help but notice a pervading scent of sulfur, a scent so characteristic and strong that it obscures all others, as I'm sure you know. Odors at the site of a fire are nothing unusual, but the added scent of sulfur can mean only one thing to a witcher – that a succubus is or was near. Finding no other traces of the beast, however, Geralt noted his suspicion and set off for the dwarven catacombs to pursue his other lead.

The witcher examined the bodies of the victims and, based on his professional knowledge, concluded that the a (sic) succubus had killed the men. Also, Geralt found a book, a tome of my poetry, on one of the corpses. Whosoever doubted that humans and beasts alike admire my oeuvre and love me, should doubt no more, as this was proof positive of my fame. In any case, the witcher had hit a dead end and came to talk to me.

The book the witcher found had been stolen from me some time before. Needless to say, I was glad to recover it. This clue suggested that the succubus was an avid fan of poetry. Thus, I had no choice but to return to the village to lure the beast out with some moving lyrics. As many an epic romance states, and as Geralt reassured me, succubi are nocturnal creatures, so the witcher and I agreed to meet at midnight.

If Dandelion doesn't sing the correct lyrics (the quest fails):

I tried to charm the succubus with sonnets to no avail, throwing my verses to the wind. The she-beast would not emerge from her den. Certain that no one could have done better in my place, I could but throw my arms up in helplessness. Thus, my career as a detective came to a premature and disappointing end.

If Geralt decides to talk to Ele'yas after meeting the succubus:

The succubus literally ate out of my hand – such was the power of my poetry. With my aid, the witcher could speak with the demon. According to the beast, the murderer was the elf Ele'yas, a jealous lover, for you must know that the succubus had many lovers, all the murder victims among them. Geralt listened to her testimony and went to speak to the elf.

Obviously Ele'yas protested his innocence. And, to be honest, Geralt and I had no evidence to prove either his or the succubus' guilt beyond a reasonable doubt. The word of a monster against the word of a bandit – the decision was hard indeed.

Siding with Ele'yas:

Geralt decided that the succubus – guilty or not – was too dangerous to leave alive. He proceeded to kill the beast. The case was thus closed, but the mystery was never fully unraveled. To this day we cannot be certain who was killing the young men, even though the succubus was the more likely perpetrator. Having fulfilled the contractor's wish, Geralt went to see Ele'yas about his reward.

Ele'yas seemed content that the succubus was dead, though it might be more accurate to say he was not unmoved. His face seemed to express an entire range of emotions, so many, in fact, that the witcher could not ascertain if the elf had detested the she-beast or now mourned her. Be that as it may, Ele'yas rewarded Geralt for his toil, and the case proved entirely profitable for the witcher. I cannot say if there were no more murders in Vergen. Fate in all its fickleness soon sent us off on other adventures, and I received no more news from Vergen.

Siding with the succubus:

Geralt decided to accuse Ele'yas. He presented what little evidence we had gathered to Iorveth. The Scoia'tael leader wanted to talk to his subordinate, but Ele'yas was far away by then – he had fled. Still uncertain of the elf's guilt, the witcher went to tell the succubus everything.

Geralt decided that Ele'yas – guilty or not – would sooner or later kill the succubus. The witcher's discussion with the elf quickly escalated into a fight, and Geralt slew the Scoia'tael. We will never know if Ele'yas was truly the murderer, yet we think this very likely. Either way, the witcher decided he deserved some reward and went to see the succubus about it.

I will not describe how the succubus rewarded Geralt. I leave that to your imagination, dear reader. I will note only that the witcher seemed more satisfied than he usually was upon receiving a bulging pouch of orens. All in all, the adventure with the she-beast ended well for us. Were there no more murders in Vergen? That I do not know, for we were soon forced to leave the proud dwarven town and, alas, I received no more news from there.